CONCLUSIONS TO BE DRAWN FROM FOSSILS. 55 
head are really based upon the present distribution of animal 
and vegetable life on the globe, and are therefore liable to be 
vitiated by the following considerations :— 
a. Most fossils are extinct, and it is not certain that the 
habits and requirements of any extinct animal were exactly 
similar to those of its nearest living relative. 
6. When we get very far back in time, we meet with groups 
of organisms so unlike anything we know at the present day as 
to render all conjectures as to climate founded upon their sup- 
posed habits more or less uncertain and unsafe. 
¢. In the case of marine animals, we are as yet very far from 
knowing the exact limits of distribution of many species within 
our present seas ; so that conclusions drawn from living forms 
as to extinct species are apt to prove incorrect. For instance, 
it has recently been shown that many shells formerly believed 
to be confined to the Arctic Seas have, by reason of the ex- 
tension of Polar currents, a wide range to the south ; and this 
has thrown doubt upon the conclusions drawn from fossil 
shells as to the Arctic conditions under which certain beds 
were supposed to have been deposited. 
d, The distribution of animals at the present day is certainly 
dependent upon other conditions beside climate alone; and 
the causes which now limit the range of given animals are 
certainly such as belong to the existing order of things. But 
the establishment of the present order of things does not date 
back in many cases to the introduction of the present species 
of animals. Even in the case, therefore, of existing species of 
animals, it can often be shown that the past distribution of the 
species was different formerly to what it is now, not necessarily 
because the climate has changed, but because of the alteration 
of other conditions essential to the life of the species or con- 
ducing to its extension. 
Still, we are in many cases able to draw completely reliable 
conclusions as to the climate of a given geological period, by 
an examination of the fossils belonging to that period. Among 
the more striking examples of how the past climate of a region 
may be deduced from the study of the organic remains con- 
tained in its rocks, the following may be mentioned: It has 
been shown that in Eocene times, or at the commencement 
of the Tertiary period, the climate of what is now Western 
Europe was of a tropical or sub-tropical character. Thus the 
Eocene beds are found to contain the remains of shells such 
as now inhabit tropical seas, as, for example, Cowries and 
Volutes ; and with these are the fruits of palms, and the 
remains of other tropical plants. It has been shown, again, 
